1. Field of the Invention
The present invention generally relates to electric power generation using renewable sources of energy, and more particularly to enhanced uses of wind or solar energy in combination with geothermal fluids originating in hot strata of the earth's mantle as a source of heat for operating steam-driven turbine generators. The system, apparatus, and methods disclosed herein utilize wind or solar generated electricity, hydrogen gas, and optimized parameter control to exploit the heat energy available from geothermal fluids in providing efficient generation of electric power with a very low carbon footprint and near zero emissions into the atmosphere.
2. Background of the Invention and Description of the Prior Art
Use of the heat energy in geothermal fluids such as dry or wet steam from deep production wells into the earth's mantle (“hydrothermal resources,” as described in an article entitled Geothermal Power Stations, by Lucien Y. Bronicki, in the Encyclopedia of Physical Science and Technology, Third Edition, 2002, Robert A, Meyers, Editor-in-Chief, Volume 6, pp. 709-719.) as a source of heat to drive steam turbine electric generators is an active area for renewable energy development and research. Conventional approaches endeavor to extract as much heat energy as possible from the geothermal fluids before returning them via injection to locations beneath the surface of the earth where the fluids may reacquire heat energy from the hot rock strata.
Conventional electric generating facilities such as natural gas-fired or coal-fired generators are of questionable utility to meet future electricity needs because they burn carbon based “fossil” fuels and oxygen. In addition to having a large and undesirable carbon “footprint,” such facilities produce as undesirable byproducts carbon dioxide and nitrous oxide, believed to be among the principle contributors to climate change and air pollution. In addition, these fossil fuel generating facilities are expensive to construct. Nuclear-fueled generators, though having a small carbon footprint and low atmospheric emissions, are extremely expensive to build and operate, and present the additional problems of disposing of the nuclear waste. Nuclear power generating plants are also faced with dissipating large amounts of waste heat. Thus, the prospects of relying on fossil fueled or nuclear fueled electric power plants to meet the future electricity needs of a growing population with minimal effects on the earth's environment at a reasonable cost are unpromising. New ways of generating and distributing electric power must be developed and made available to the distribution grids.
In looking to other sources of energy for generating electricity, particularly renewable sources, one must keep in kind that there are many variables in the generation and distribution of electric power. Demand peaks and ebbs in response to temporal and climate cycles. The output of wind powered generators as shown in FIG. 1 is subject to vide variations in climate conditions. Moreover, the temperature and heat content of geothermal fluids—principally steam, but may also include water and brine solutions of varying composition—varies widely according to geographic and geological diversity, as well as the depth and suitability of production wells. While advances are being made in harnessing the extremely abundant solar energy, inefficiencies and problems of scale continue to challenge development efforts.
In FIG. 1, there is illustrated in simplified form a conventional wind-powered electric generator system 10 that is typical of the prior art. In the system 10, an electric generator 12 is rotated by a wind-driven propeller 14 to generate an electric voltage that is conducted to a distribution grid 16 (not shown) along wires 18. The wires 18 may typically be supported by a plurality of towers 20 spaced at substantially uniform distances to connect the generator output to the distribution grid 16. In a typical wind farm, many such wind generator systems 10 may be employed, their outputs coupled to the distribution grid via direct wires 18 as shown or via wires to a substation (not shown, because it is well known in the art), which in turn may be connected to the distribution grid 16. The elements of such a wind power generating system 10 and distribution grid 16 are well known and will not be further described herein.
In a basic, prior art electric power plant that utilizes geothermal fluids, one example of which is shown in simplified form in FIG. 2, dry steam or high temperature water from geothermal production wells is used to drive a steam turbine and electric generator. The geothermal fluid for use as a working fluid to drive a turbine may be obtained from any deep natural gas, oil, water, geothermal well, etc. having sufficient heat at depth. Note that a working fluid in this context may be either a liquid or a vapor (such as dry steam). In a dry steam plant, the turbine is driven directly by the geothermal steam. In a flash steam plant, high temperature fluids are first vaporized in an expansion chamber at low pressure and the water vapor is used as a working fluid to drive the turbine. Since many production wells produce geothermal fluids of moderate temperature, e.g., less than 200° C., the geothermal fluid may be routed through the primary side of a closed heat exchanger in a third type of power plant called a binary-cycle power plant.
In a binary cycle geothermal power plant, illustrated in basic form in FIG. 2, a second working fluid, such as an organic working fluid that boils at a lower temperature than water, is conducted through the secondary side of the heat exchanger. A few examples of organic working fluids include ammonia, isopentane, isobutane, etc. Heat from the primary side geothermal fluid is transferred to the secondary “organic” working fluid that is used to drive the turbine. A given geothermal power plant may employ one or more turbine/generator combinations. The output of the generator is connected to an electricity grid for distribution and the spent steam is typically injected into the earth via an injection well.
The system 30 shown in FIG. 2 includes an electric generator 32 whose electric output is coupled to the distribution grid 16 via wires 34. The generator receives its driving force from the rotating output shaft 38 of a steam driven turbine 36. The steam driven turbine 36, a well-known structural component, converts high temperature, high pressure steam to the mechanical rotation of its output shaft 38. The steam, also called the working fluid, is applied to an inlet 40 of the steam turbine 36 via a conduit 44, which carries the working fluid in a circulating loop. The working fluid is chosen to have a lower boiling point than the geothermal fluid, which most commonly has a temperature between 150° C. to 200° C., although some hydrothermal deposits may range from under 100° C. to as high as 350° C. The working fluid receives heat energy by passing through a heat exchanger 50, where heat is transferred to the working fluid flowing in conduit 44. This transfer of heat causes the working fluid to vaporize. In the heat exchanger 50, the hotter geothermal fluid flows through internal passages in close proximity to the passages conveying the cooler working fluid to facilitate the transfer of heat into the working fluid. The heat exchanger 50 has a source side 52 and a demand side 54, referring respectively to the source of heat to operate the turbine and to the loading or demand for electricity on the output of the generator 32. The geothermal fluid is obtained from deposits 60 via production wells 62 and pumped by a pump 64 through a conduit 66 and the source side 52 of the heat exchanger 50. After giving up some of its heat in the heat exchanger 50, the cooled geothermal fluid is returned to the Earth via a conduit 76 and an injection well 72 into deposits 70 similar to or adjacent to the original deposits 60.
The use of two separate fluids in the power plant of FIG. 2 enables isolation of the fluid used to drive the turbine 36 from the fluid produced from the production wells 62 and thus gives rise to the term “binary cycle” power plant. A binary cycle power plant thus prevents the often caustic, corrosive, or abrasive substances that may be contained in the geothermal fluid from damaging the internal components of the turbine 36. The working fluid may be water, or low temperature steam, or an organic fluid material such as isobutane, isopentane, propane, or other easier-to-condense hydrocarbons. These organic compounds may be used because of their relatively low boiling points. The geothermal fluid may be high temperature steam, hot water, high temperature brine, a mixture of these fluids, or a mixture containing one or more of these and other elements, minerals, or hydrocarbon compounds.
While these prior art plants can provide electricity from renewable sources with zero emissions, they are subject to inefficiencies and variable outputs because of the variability in temperatures of the geothermal working fluids. Such systems are adequate for steady state electricity loads but are much less suited to meeting the demands for both base loads and peak loads, and levels of demand intermediate base and peak loading. Accordingly there is a need for electric power generation systems that rely on renewable sources and provide electricity output responsive to wide variations in demand despite potentially wide variations in the energy resources from which the electricity is derived. Additionally, it is preferred that the system operate with zero emissions into the atmosphere or into the earth's water resources. Moreover, it is further preferred that the system be configured to operate with improved efficiency and to minimize the waste of heat or unused constituents of the working fluids obtained from the deep wells or other resources.